On known machines for cellophaning packets of cigarettes, a sheet of heat-seal wrapping material is folded against one wall of the product, and at least two portions of the sheet of wrapping material superimposed one on top of the other; and a sealing surface of a sealing head is then brought into and maintained for a given length of time in contact with the superimposed portions to seal the portions together and stabilize the sheet of wrapping material in the folded configuration.
On known cellophaning machines, the sealing surface of the sealing head is maintained constantly at an operating temperature which gets closer to the melting temperature of the heat-seal material in direct proportion to the increase in the operating speed of the machine.
When the sealing surface is brought rapidly into contact with the superimposed portions of the sheet of wrapping material and the temperature of the sealing surface is close to the melting temperature of the heat-seal material, the portions of the sheet of wrapping material contacting or close to the sealing surface tend to crease and/or become undulated, thus seriously impairing the appearance of the wrapping. This problem is particularly noticeable on modern cellophaning machines operating at very high speeds of over 500 packets a minute.